Plugin Alliance are running the Advent Calendar of special one day offers. Each day they make one plugin available at a very special price. On December 1st it was the Lindell 254E for $79 instead of $149 but that door has been closed for now.
Two Current Special Offers
Due to the world wide time zones they are offering every plugin for up to 48 hours. They start every promotion when a new day starts in New Zealand, and they end it when the day is over on Hawaii. It´s the only way they can make sure everybody can make use of every deal.
So right now in the '2' window there is the enysia nvelope plug-in available at $99 instead of $199 but this won't last long.
Behind the '3' window is the Brauinworx bx_dude at $49 instead of $149.and that will be available until the end of Dec 3rd in Hawaii.
So the best thing to do is check out the Plugin Alliance calendar and see if they are offering a plug-in you are looking for.